There are practical concerns that could dissuade other Democrats from challenging Vice President Kamala Harris's campaign for president, former New Jersey Gov. Chris Christie, an ABC News contributor, told ABC News Live on Sunday.

"There are such practical concerns for the people who might be thinking about challenging the vice president. None of them have national campaigns organized, none of them have one state director in any one of the 50 states, none of them have a national fundraising operation," Christie said.

"I think she'll be able to inherit the money that is in the Biden-Harris campaign right now," Christie said.

Christie added that anyone considering running will wonder if they will be able to beat a candidate who is a sitting vice president who has been endorsed by the sitting president.

"Most of the people who would be serious candidates, I think, quite frankly, they are going to look at this and say 'I hope she picks me for No. 2' and move on from there," Christie said.

"I don't think there is going to be any challenge to Kamala Harris," Christie said.

On the heels of President Biden's departure from the 2024 presidential race Sunday, two major Democratic donors -- Reid Hoffman and Alexander Soros -- publicly endorsed Kamala Harris as the next candidate.

"The Democrats are the party of policy, progress, and action. When presented with the choice between Kamala Harris and Donald Trump, I believe in the American people to make the right decision for our country," Hoffman wrote in a statement on X.

Hoffman cofounded professional networking site LinkedIn in 2003 and is a partner at venture capital firm Greylock Partners.

"The Biden-Harris administration has put this country on the right track. It’s time for us to unite. I wholeheartedly support Kamala Harris and her candidacy for President of the United States in our fight for democracy in November," he continued.

Soros, one of five sons of billionaire George Soros, took to X to share a photo of himself with Harris, writing: "It’s time for us all to unite around Kamala Harris and beat Donald Trump. She is the best and most qualified candidate we have. Long live the American Dream! #Harris2024"
-ABC News' Soorin Kim, Will McDuffie, Gabriella Abdul-Hakeem, Fritz Farrow

Dozens of current and former Democratic National Committee members are endorsing Harris.

Sixty-three signatories had joined onto the letter, which was obtained by ABC News, as of early Sunday evening, but more signatures could be added.

"We are deeply grateful to President Biden and his family for their decades of service to our nation, including the decision he made today to pass the torch of the Democratic nomination and American democracy itself to a new generation of public servants. We strongly and enthusiastically endorse Vice President Kamala Harris -- the candidate with the best experience and capacity to unite our Party and the United States -- for the Democratic nomination for President of the United States. We ask that you join us," they wrote.

The International Association of Fire Fighters, which was the first union to back Joe Biden in the 2020 presidential election, released a statement on his decision to exit the 2024 race.

"Past, present, and future fire fighters are better off because of Joe Biden," IAFF general president Edward A. Kelly said Sunday.

"For nearly 50 years, he has been a champion of the IAFF. His work has directly led to the hiring of tens of thousands of fire fighters, safety improvements in this most dangerous of jobs, and a nation that is now aware of the toxic threats we face every time we put on our gear," Kelly said.

"And, when a fire fighter makes the ultimate sacrifice, President Biden’s work has ensured their families receive the benefits they deserve," Kelly continued.

Kelly called Biden the "greatest President fire fighters and emergency medical workers have ever had."

"Our membership – and the communities we serve – will forever be in his debt," Kelly said.